Background Recent studies have found that manganese is closely related to the development of liver disease, but its pathogenesis has not been elucidated. The role of autophagy in liver diseases is controversial. As an autophagy blocker, 3-methyladenine (3-MA) can regulate autophagy levels, which provides clues for revealing the mechanism of manganese-induced liver injury.

Objective This study is designed to reveal the damage effect of subchronic manganese exposure on the liver of C57BL/6 mice, and to elucidate the key role and mechanism of subsequent autophagy in cells.

Methods C57BL/6 mice were used to establish a subchronic manganese exposure model. The animals were randomly divided into four groups with 14 animals in each group:control group, manganese exposure group, 3-MA treatment group, and manganese exposure combined with 3-MA intervention group. The control group was intraperitoneally injected with normal saline (0.01 mL·g^-1); the manganese group was intraperitoneally injected with 15 mg·kg^-1 manganese chloride (four times per week); the 3-MA treatment group was intraperitoneally injected with 7.33 mL·g^-1 3-MA (three times per week); the manganese exposure combined with 3-MA intervention group was injected with 15 mg·kg^-1 manganese chloride for 30 min before 7.33 mL·g^-1 3-MA. Relevant indicators were tested immediately after modeling. Liver histological changes were observed with HE staining. The injury of hepatocytes and the changes of autophagic lysosomes in liver tissues were observed under transmission electron microscope. Blood manganese level was detected using atomic absorption spectrophotometer. The changes of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels were detected using automatic biochemical analyzer. The apoptosis level of hepatocytes was evaluated with TdT-mediated dUTP nick end labeling (TUNEL) staining. The expressions of autophagy related proteins LC3-II and Beclin1 were detected by Western blotting.

Results The HE staining results showed that compared with the control group, there were more inflammatory cell infiltration in the intracellular space and more binucleate cells in the manganese exposure group; after 3-MA intervention, the liver inflammatory infiltration and liver injury induced by manganese exposure were reduced. The transmission electron microscopy observation showed that mitochondria in liver cells of mice exposed to manganese were swollen and vacuolated, and more autophagic lysosomes were to be degraded; after 3-MA intervention, the vacuolization of mitochondria and the number of autophagic lysosomes were decreased. Compared with the control group, the levels of blood manganese, ALT, and AST in the manganese exposure group were increased (P < 0.01); after 3-MA intervention, the increased ALT and AST levels were reduced (P < 0.01). The Western blotting results showed that compared with the control group, the expression levels of autophagy related proteins LC3-II and Beclin1 were increased in the manganese exposure group (P < 0.01); compared with the manganese exposure group, the protein expression levels were reduced in the combined 3-MA intervention group (P < 0.01). The TUNEL staining results showed that compared with the control group, the apoptosis hepatocytes in the manganese exposure group were increased (P < 0.01); compared with the manganese exposure group, the apoptosis hepatocytes in the combined 3-MA intervention group were reduced (P < 0.01).

Conclusion Subchronic manganese exposure can induce an elevation of autophagy in mouse hepatocytes, accompanied by liver injury and liver function decline, and treatment with autophagy inhibitor can reduce liver damage in manganese exposed mice, suggesting that liver cell damage induced by manganese exposure may be partially resulted from autophagy.